First the general advice: If your ninja equipes a dancing knife, equip it at your left hand, because it activates after the right hand attack.

Now the combo. Twin lance at your right hand and dancing knife at your left.

Suppose your dancing sword activates. Then the attack is something like this. 800 * 2 damage from your lance, then the sword dance activates, then your twin lances do 3200 * 2 more damage. The dessert is the 2000 damage from the dancing dagger.

The grand total is a whopping (more or less) 10000 damage.

Not bad.

I know the combo only works like a 12.5 %, but this is one reason why you have return.